Manganese is an important mineral, required in small quantities in the human body. Though it is abundantly found in nature, the human body contains only traces of this essential element. Most of the manganese in the body is concentrated in the skeleton, brain, liver and pancreas.
The importance of manganese has been recently recognized and it is now considered an essential nutrient in human nutrition. Manganese not only functions as an important constituent of some enzymes, it also acts as an activator of some other enzymes.
Manganese acts as an antioxidant, as part of the important enzyme, manganese super oxide dismutase (MnSOD). This enzyme prevents oxidative damage to the cells by converting the reactive super oxide to other harmless compounds. Manganese is an activator of some enzymes which are required for the metabolism of proteins, fats and carbohydrates. It helps the body synthesize cholesterol and is involved in reproduction and healthy bone growth.
Other functions of manganese include proper brain function, role in wound healing as it is required for formation of collagen, optimal functioning of thyroid gland, synthesis of sex hormones and blood sugar regulation.
 Food Sources
Whole grains are one of the richest sources of manganese. However, milling or refining considerably lower the manganese content of these grains. Leafy vegetables like spinach and mustard greens are also very rich sources, though the oxalates in spinach inhibit manganese absorption to a certain extent.
Nuts, fruits like bananas, pineapple and figs, vegetables like leeks and broccoli are also good dietary sources of manganese. Black tea provides a considerable amount of manganese, though the tannins in tea moderately reduce its absorption.
 Recommended Dosage
There is not enough information to establish the recommended dietary allowances (RDA) for magnesium. Instead, Adequate Intake (AI) levels for manganese have been given in 2000 by the Institute of Medicine at the National Academy of Sciences. These values on a daily basis are as follows:
- 0-6 months: 3 micrograms
- 7-12 months: 600 micrograms
- 1-3 years: 1.2 milligrams
- 4-8 years: 1.5 milligrams
- Boys 9-13 years: 1.9 milligrams
- Boys 14-18 years: 2.2 milligrams
- Girls 9-13 years: 1.6 milligrams
- Girls 14-18 years: 1.6 milligrams
- Men 19-70 years: 2.3 milligrams
- Men greater than 70 years: 2.3 milligrams
- Women 19-70 years: 1.8 milligrams
- Women greater than 70 years: 1.8 milligrams
- Pregnant women 14-50 years: 2 milligrams
Manganese deficiency is rare in humans, though it has been demonstrated in animals. Since manganese takes part in a number of reactions in the body, its deficiency affects various systems and their functions. The symptoms associated with manganese deficiency in humans include, low cholesterol levels, skin rash, weight loss and impaired growth, hair loss and dizziness. In children, manganese deficiency can cause skeletal deformities and bone demineralization.
Manganese toxicity from dietary sources has not been reported, even though vegetarian diets, predominantly consisting of unrefined cereals, can provide a high content of manganese. Workers involved in manganese processing industry are at maximum risk of toxicity due to inhalation of manganese dust. Symptoms take months and sometimes years to appear, and affect the nervous system the most. They include irritability, aggressiveness and hallucinations, which may proceed to a more serious condition with tremors and difficulty in walking similar in Parkinson’s disease.
Individuals with liver failure are at an increased risk of manganese toxicity, as liver is responsible for removing the excess manganese in the body. The Institute of Medicine at the National Academy of Sciences has established the Tolerable Upper Intake Levels (UL) for manganese which is as follows:
- Infants: not established (no supplemental manganese should be given)
- 1-3 years: 2 milligrams
- 4-8 years: 3 milligrams
- 9-13 years: 6 milligrams
- 14-18 years, including pregnant and lactating women: 9 milligrams
- Greater than 19 years, including pregnant and lactating women: 11 milligrams